In order to solve the ozone problem, we need a firm research basis from which to make decisions. Many people hold the misconception that scientists fully understand atmospheric chemistry and dynamics. In fact much remains unknown. For example, some estimates of ozone precursors released into the air by various human activities disagree by orders of magnitude. We don’t yet know as much as we need to know about ozone chemistry at night, nor about the transport of gases between the lower and upper reaches of the atmosphere. We have a great deal to learn about connections between air quality and climate, and we still cannot predict our chemical weather.
Atmospheric chemists measure ozone at ground level, in the air with balloons and aircraft, and from space with Earth-orbiting satellites. Each vantage point offers a different perspective, a different geographic scope, and usually a different degree of spatial resolution.
Measurements on the ground contribute chiefly to understanding specific localities because ozone levels change so much from one locality to another and from one day to the next. The EPA, along with states and local air agencies, has established a number of monitoring networks to collect air quality data. One network of Photochemical Assessment Monitoring Stations (PAMS) collects and reports detailed data for NOx, volatile organic compounds, ozone, and meteorological conditions for areas in the United States that have the most severe and persistent ozone problems. The State and Local Air Monitoring Network (SLAMS) and the National Air Monitoring Network (NAMS) also track ozone air quality across the country.
Balloons and aircraft give us a regional view, though still rather limited in space and time. They make virtual lines of data points through the atmosphere. Much of the perspective needed for inter-regional and global studies comes from satellites. Space-based instruments on satellites help us understand how ozone travels from one region to the next, and from one continent to another. Satellites collect data over the entire globe at far less cost than a network of ground-based systems could achieve over a fraction of the area. We are just beginning to explore the capacity of satellites to identify sources of air pollution and where polluted air travels. NASA’s Aura satellite, scheduled to launch in 2004, will make a big leap in that capability.
Satellite mission teams are improving their capability to pinpoint ozone precursor sources and to track their movements, particularly as scientific teams collaborate on corresponding field campaigns with balloons and aircraft. Integrating and comparing ground-based, balloon, aircraft, and satellite measurements is a crucial step in achieving an accurate and complete story of ozone chemistry, and it is a major focal point for current research.
Long-term, consistent monitoring is essential, because some changes in the atmosphere happen very slowly and trends are often obscured by the wide variability of measurements and climate. Several satellites are in orbit or will launch in the near future to look at complex tropospheric ozone chemistry. In 2004, the Aura satellite will carry a payload of four instruments, each of which will measure ozone or its precursors in different and overlapping ways. Taken together, data from the instruments on Aura will provide rich new sources of information on the horizontal and vertical distribution of key atmospheric pollutants and greenhouse gases and how their distributions evolve and change over time. Further, combining Aura data with data from other missions will reveal even more information on these and other important issues.